The invention relates generally to weighing systems and deals more particularly with an apparatus for levelling product while being fed to a container for subsequent weighing, which apparatus may be combined with a combination weighing machine.
A previously known combination weighing system comprises a vibrating dome or inverted cone which receives product from an input conveyor located above it. The product is dumped onto the dome, and the vibrations cause it to slide by gravity down the sides of the dome. A plurality of vibrating chutes which are downwardly inclined from the base of the dome guide the product to an equal number of temporary storage containers or time-fill buckets. Each of the time-fill buckets receives a charge of the product at a relatively slow rate and then dumps the charge instantaneously into a weighing hopper of a weighing scale. There, the charge is weighed and considered in a subsequent combination search aimed at locating a combination of the scales which yields a total weight at or slightly above a target weight.
The angle of incline of the vibrating chutes, the amplitude and duration of the vibrations of the chutes and the characteristics of the product influence the feed rate to the time-fill buckets. The range of quantities of product which are deposited in the time-fill buckets determines the typical number of scales which are combined to yield the target weight. For example, if the target weight is 80 grams and 15 to 25 grams of product are deposited in each time-fill bucket and subsequently into the associated weighing scales, then the product in 3-5 weighing scales will ordinarily be combined to yield the target weight. With this range of product in each weighing scale, there are a large number of possible combinations of scales which conceivably may yield the target weight and this large number provides a very accurate weighing system. If there were substantially more product in each scale than the 15-25 gram desired range, then there would be fewer viable combinations of scales which will conceivably yield a combined weight near to the target weight so that the accuracy of the system on the average will decline. Consequently, it is desirable to provide charges of product in the aforesaid range.
A problem has arisen in the feeding of certain types of products which tend to clump. One example is looseleaf chewing tobacco which tends to clump because of its inherent stickiness and the elongated, irregular shapes of the leaves which tangle with one another. Another example is lollipops which are also inherently sticky and have stems and wrappers which may catch one another. Still another example is frozen clam strips which tend to clump because of the inherently sticky surface of the strips and their elongated shape.
Focusing on the looseleaf chewing tobacco application, as the tobacco is fed along a vibrating chute of a combination weighing system, the product may clump to a height of 12 centimeters even though the desired and normal height of the product on the chute is only 2-3 centimeters. Such clumps may weigh 50-100 grams, and in the aforesaid application where the package target weight is 80 grams, the weight of one clump alone in a weighing scale may prevent the scale from participating in a combination, degrade the accuracy of the combination weighing system, and increase the incidence of lock-up, a condition in which no combination of scales meets the weight range criteria.
Previously, a rotating tine assembly has been installed above the input conveyor to provide some control over the height of the product on the input conveyor and its feed rate onto the vibrating dome. The assembly comprises a plurality of tines mounted in rows to a common shaft. The shaft is rotatably mounted to a bracket which bracket is fixedly mounted in place. The tips of the tines may be curved and periodically pass over the product on the input conveyor close enough to engage relatively high clumps of the product but far enough to miss the product when traveling at a normal height. The assembly rotates counter to the movement of the product on the coveyor belt so that the tines rake back the peaks of the clumps. Occasionally, a clump is so high that the tines lift it and catapult it over the assembly downstream of the assembly. While this assembly provides some control over the height of product and resultant feed rate, improvements are deemed necessary to provide a finer control on the product height and feed rate. Also, certain types of products such as looseleaf chewing tobacco tend to stick to the tines and adjacent portions of the weighing system and improvements are deemed necessary to provide easier means for cleaning the tines and adjacent portions of the weighing system. Moreover, much of the clumping results from the dropping of product from the input conveyor onto the vibrating dome and such clumps cannot be dissipated by the aforesaid tine assembly when mounted above the input conveyor.
A general object of the present invention is to provide an apparatus for controlling the height of a product subject to clumping in a product feed assembly and the resultant feeding rate more accurately than previously provided.
A more specific object of the invention is to provide an apparatus of the foregoing type which controls the feed rate from a vibrating chute of a combination weighing machine to a time-fill bucket.
Another general object of the present invention is to provide an apparatus of the foregoing type which does not impede access to adjacent portions of the product feed assembly.